An investigation of tear film physiology in human and animal eyes has been undertaken. The isolation, identification, and characterization of aqueous tear components and conjunctival mucin by various biochemical and surface chemical methods are in progress. Molecular weight, isoelectric point, carbohydrate and possible lipid content are to be determined. The major fraction of tear proteins (greater than 50 percent) has an average molecular weight similar to that of albumin. The fraction containing the largest molecular weight proteins (about 400,000 daltons) is relatively minor, about 4 percent of the total protein content. This fraction contains five different components as distinguished by ion-exchange column chromatography and is believed to contain the active component(s) responsible for tear film stability. A similar protein fraction containing some carbohydrate has been found in mucoid clots. The analysis of conjunctival mucus and goblet cell content from calf eye conjunctiva is also in progress. Model systems to assess meibomian lipid - tear protein interaction and lipid-masking ability of tear proteins have been developed and used to evaluate artificial tears. Investigation of the physiological causes of poor contact lens tolerance yielded further insight into the mechanisms underlying tear film stability and implicated tear flow dynamics.